Process of making cyanids.



No. 792,260. PATENTED JUNE 13, 1905. J. GROSSMANN.

PROCESS OF MAKING GYANIDS.

APPLIUATION FILED FEB. 7, 1905.

UNITED STATES Patented June 13, 1905.

PATENT CEEIcE.

JACOB GROSSMANN, OF MANCHESTER, ENGLAND, ASSIGNOR TO THE GROSSMANN CYANIDE PATENTS SYNDICATE LIMITED, OF MAN- CHESTER, EN GLAND.

PROCESS OF MAKING CYANIDS- SPECIFICATION forming part of Letters Patent N0. 792,260, dated June 13, 1905.

Application filed February '7, 1905. Serial No. 244.673.

To (all 1071,0712 it may concern.-

Be itknown that I, J ACOB GRossMANN, a citizen of Great Britain, residing at Harpurhey, Manchester, in the county of Lancaster, England, have invented certain new and useful Improvements in and Connected with the Manufacture of Cyanids, of which the following is a full, clear, and exact description.

The object of this invention is to prepare cyanids more economically from ferrocyanids than it has been done before. An invention for a somewhat similar purpose is the subject of an application, Serial No. 152,952, filed April 16, 1903, for Letters Patent for improvements in and connected with the manufacture of cyanids. In that application I have shown that the insoluble residue of metal ferro-ferrocyanid obtained by the decomposition of ferrocyanids with mineral acids can be quantitatively reconverted into ferrocyanid by boiling with a caustic alkali in the presence of air in excess. I have found that the very same result can be attained if the caustic alkali is replaced by an alkaline carbonate in the presence of air in excess, and that improvement forms the subject of the present application.

It has been known for many years that on distilling two molecules ferrocyanid of potash with from three to six molecules dilute sulfuric acid hydrocyanic acid is evolved and an insoluble compound of potassium ferro-ferrocyanid is formed. It has also been known for many years that thatinsoluble residue thus produced may be partly reconvcrted into ferrocyanid of potash by boiling with an alkaline carbonate; but no method was known whereby these isolated reactions could be combined in such a manner that they would ultimately yield all the cyanogen contained in ferrocyanid of potash as hydrocyanic acid in practically quantitative proportions, nor was it known that other ferrocyanids besides the potassium ferrocyanid follow the same law.

By experimentingon a commercial scale with large quantities of material and under such conditions as are the only practicable ones in dealing with such a poisonous substance as hydrocyanic acid on a large scale, I have been able to devise a method and plant by which I can manufacture cyanids of good commercial quality by distilling ferrocyanids with sulfuric acid, absorbing the prussic acid evolved in alkali, and reconverting the metal ferro-ferrocyanid formed into ferrocyanids in which :20 represents any figure up to three. Thus one half of the total cyanogen should be made available as hydrocyanic acid for the preparation of cyanids, While the other half should be obtained in the form of the insoluble metal ferro-ferrocyanid, which is generally termed Everitts salt; but this reaction does not take place regularly according to the equation, and therefore varying quantities ofhydrocyanic acid are evolved. I have, however, ascertained that Whatever the yield of hydrocyanic acid the resulting Everitts salt contains exactly the amount of cyanogen corresponding to the difference between the total cyanogen originally contained in the ferrocyanid and that evolved as hydrocyanic acid in such a form that it can be practically quantitatively reconverted into alkali ferrocyanid. I have,

moreover, found that for the purpose of my process two molecules of ferrocyanid to three molecules of sulfuric acid (with about five per cent. of the latter in excess) are most prac ticable, as the waste liquors are almost neutral.

The equation which is given in text-books as representing the action of alkali carbonate i 0., ferrocyanid and ferrous hydrate are formed; but the quantity of ferrocyanid reconverted is far below theory unless a large excess of alkali carbonate be used and boiling prolonged for an impracticable time, while the air is excluded so as to obtain the ferrous hydrate according to the equation; but] have found thati'f care is taken to supply sufficient air during the boiling to produce, not the ferrous hydrate, but a higher oxid of iron, this reaction takes place quantitatively with a very small excess of alkali carbonate and in a very short time. My reaction is therefore as follows:

The conversion of the hydrocyanic acid into cyauid of potassium may be expressed by the equation As long as the temperature does not rise too high the absorption of the hydrocyanic acid by caustic-alkali solution is almost complete. 1 find the same to be the case with caustic lime or milk of lime, which produces calcium cyanid. l have also found that sodium ferrocyanid behaves exactly like the potassium ferrocyanid as regards the evolution of hydrwyanic acid and as regards the relation in the composition of the resulting sodium ferrofcrrocyanid and the quantity of hydrocyanic acid evolved. Mixtures of potassium and sodium .ferrocyanid also behave analogously. So do double salts, such as calciuni-potassium 'ferrocyanid and similar compounds. I. have also found that carbonate of soda behaves analogously to carbonate of potash in the conversion of metal ferro-ferrocyanid into ferrocyanid. So do mixtures of carbonate of soda and potash.

it appears from the foregoing that my invei'ition comprises a combination of the following operations: first, distillation of hydrocyanic acid; second, absorption of the hydroryanie acid and further treatment of the resultingcyanid solution; third, reconversion of the metal ferro-ferrocyanid. These operations are carried out on a large scale as follows:

I'll-M. Dist/U (1/ /1111 0 7" 71.;1 (1/00 1/Hi0 (1c; Z. I have found that lead is not acted on either by the mixture of ferrocyanid and sulfuric acid or by hydrocyanic acid, and I therefore prefer to carry out this operation in a still madeof lead; butenameled iron or other suitable material may be used for its construction when it is advisable to do so. Separate pipes for the supply of live steam, air, sulfuric acid,

other suitable material and fitted with suit' able agitating machinery. The whole system is at its outlet connected with a Kortmg ex hauster or similar apparatus for producing a partial vacuum or for drawing air through under a partial vacuum or otherwise.

A suitable apparatus to be preferably used for the distillation of the hydrocyanic acid is shown in the accompanying drawing.

A is a still, preferably made of lead.

(t and c are pipes leading from the storage vessels 0 and 1) into the still and convey sulfuric acid and the solution of ferrocyanid, respectively, into that still.

For heating the still live steam is conveyed to it by the pipe 6, whereas the still is emptied by means of the running-off pipe (Z. The byd rocyanic acid evolved passes through the dephlegmating or condensing tower B, whence it goes forward first into the absorption vessel l thence into the absorption vessel F, and finally into the absorption vessel (1 all of which are charged with a solution of caustic alkali. The last traces of hydrocyanic acid are retained in the vessel Gr with perfectsa fety. /t is a Korting injector connected to the last absorbing vessel, by which a partial vacuum is produced, which is maintained in the whole apparatus while the process of distillation is going on.

\Vhen an operation is commencing, the necessary quantity of hot saturated solution of ferrocyanid of potaslncontaining about twenty-five percent. of crystallized ferrocyanid, is run into the still, (which in a continuous process will be still hot from a previous opera tion,)all the taps are closed, and the exhauster is set to work so as to keep up a partial vacuum of about four inches of mercury. The taps for live and confined steam are then turned on and the acid, which contains about twenty-five per cent. H2501, is run in slowly at the rate of about one gallon per minute or slower. three to live per cent. in excess of the quantity necessary to form the three molecules of neutral potassium sulfate, corresponding to two molecules of ferrocyanid. The amiaratus works very regularly, and when once it has been ascertained how long it takes to finish an operation it will be found that subsequent operations under the same conditions will finish in the same time. The ferrocyanid used should be reasonably free from carbonates, sulfids,

The quantity of acid used is about and other ingredients which may either interfere with the reaction in the still or influence the quality of cyanid produced.

Several stills supplied with overflows and suitably connected may be combined in such a manner as to work continuously.

During part or the whole of the operation a current of air heated or otherwise may be passed through the still.

S @0021 (Z. Abs/Hy) tion 0 f the lag (Z1 'ocycmz'c acid and fzm't/z c2 trcaMmnZfQft/Lc 'rcsultzhzg cymticl .s-0Z'ut0n.The absorption vessels are closed boxes or pots, made of iron or other suitable material, fitted with agitating machinery and of such size that they will hold sufficient alkaline liquors to condense the hydrocyanic acid and the vapor evolved from four or more still operations. Two, three, or more of these vessels are arranged in series, preferably at increasing heights, so that the liquid from the higher can be drawn into the lower vessel or vessels. The hydrocyanic acid enters the lower vessel first, is taken to the bottom, the gas leaves through a pipe at the top, and is drawn through the box or boxes at a higher level in the same manner. The boxes are charged with a solution of caustic soda, caustic potash, or a mixture of both. If it is desirable to produce calcium cyanid, they may be charged with milk of lime, and, further, slaked lime may be added after one or several operations; but in every case care must be taken that there is always slight excess of free caustic and never any free hydrocyanic acid. The temperature is regulated by cooling the absorption-pots. It is advisable to keep it below 40 centigrade. hen the first absorbing vessel is sufliciently saturated with h yd rocyanic acid, which is ascertained by test, its contents are run off into suitable covered tanks, and the pot may be recharged.

Tit/HZ. Recon 220mm f' Z720 met/711fm'rofer- IOCj/tl-H/(Zr-TllG contents of the still after distillation is linished are run into tanks and the solution of alkali sulfate separated from the insoluble residue by decantation or filtration. The alkali sulfate,which is slightly acid, is neutralized by means of calcium carbonate, alkali carbonate, or other suitable means and may then be further purified and afterward concentrated by boiling down, crystallizing, or lishing. The insoluble metal ferro-cyanid, which need not be quite free from sulfate, is made neutral by means of alkali carbonate or caustic alkali and mixed with the equivalent quantity plus about five per cent. of alkali carbonate. It is heated in suitable vessels and of such capacity as will contain the large quantity of froth which is produced during the operation either by steam or other means to boiling, is violently agitated, and air is passed through by means of a compressor or steaminjector until a test shows that all the metal ferro-ferrocyanid has been decomposed. The air may be heated or otherwise. \Vith some experience the time necessary for this can be fixed approximately for each operation after a few trials. The color of the precipitate of iron produced should be brownish-black when the operation is finished. The resulting solution of ferrocyanid may be separated from the iron compound by decantation or filtration and the latter washed free from ferrocyanid. The resulting ferrocyanid solution is carefully neutralized with suitable acid or by other means and may go back into the process either as solution or it may be further concentrated or boiled down and crystallized.

Instead of passing air through in the manner described the equivalent of agitating violently in presence of air, so as to expose the whole to its action, may be adopted, but not so advantageously.

Instead of sulfuric acid suitable acid sulfatessuch as sodium potassium bisulfate, niter cake, or similar compounds may be used.

I have so far confined myself to the action of sulfuric acid on ferrocyanids, being the most practicable form of my process in so far as it enables me to use lead for the distilling apparatus and to recover the alkali contained. in the original ferrocyanid as sulfate, which canbe made available, as described above; but it is well known that if hydrochloric, phosphoric, or similar acids are used hydrocyanic acid and metal ferro-ferrocyanid are produced, and I have found that practically the reaction takes place in the same way as with sulfuric acid and that with hydrochloric, phosphoric, and similar acids, whatever the yield of hydrocyanic acid, the resulting metal ferro-ferrocyanid contains exactly the amount of cyanogen corresponding to the difference between the total cyanogen originally contained in the ferroeyanid and that evolved as hydrocyanic acid in such a form that it can be practically quantitatively reconverted into alkali ferrocyanid.

Having now particularly described and ascertained the nature of my said invention and in what manner the same is to be performed, I declare that what I claim is- In the manufacture of cyanids from ferrocyanids, the process herein described consisting in decomposing ferrocyanids with a mineral acid, absorbing the hydrocyanic acid evolved in caustic alkali and reconverting the insoluble residue of metal ferro-ferrocyanid obtained by the decomposition of ferrocyanids with acids, into ferrocyanid by boiling with an alkaline carbonate in the presence of air in excess, substantially as described.

In testimony whereof I have signed my name to this specification in the presence of two subscribing Witnesses.

JACOB GROSSMANN.

IVi tnesses:

TIioMAs A. ANDREWS, G. E. BANNISTER. 

